John Schroeder lost everything on 9/11 - and now it's cost him his job as well.

As a hose man for Engine Co. 10, Schroeder was one of the first firefighters to respond to both the 1993 World Trade Center bombing and the Sept. 11, 2001, attacks, reaching the 23rd floor of the north tower during the latter catastrophe.

"I saw more people die that day than anyone can imagine," he told The Post.

Afterward, he struggled to cope with the staggering loss of 55 friends and colleagues. "I turned to the drink, the whole department did," he said.

Now Schroeder, 49, is one of several scarred firefighters fighting to keep their pensions because of failed drug tests, caught between the sympathy of their colleagues and the zero-tolerance policy of the Fire Department.

Schroeder tested positive for cocaine during a random FDNY drug sweep on Oct. 24, 2004. He denies using cocaine and claims he's been sober for more than a year. His lawyers argue he's a victim of a flawed test.

The department moved to fire Schroeder through a disciplinary hearing. In a highly unusual ruling, an administrative-law judge in August 2007 recommended that the 18-year veteran be allowed to retire with dignity.

Judge Kevin Casey didn't comment on the drug-test results but suggested the FDNY allow the decorated firefighter to complete his application for a disability pension. That way, Casey said, Schroeder, who suffers from lung disease that he believes came from breathing toxic Ground Zero air, could keep his health benefits.

At almost the same time, another 9/11 firefighter, Thomas Kelly, was undergoing a similar trial. Kelly admitted after a failed drug test that he had used cocaine. He argued that dismissal and loss of his pension and benefits was too harsh a penalty. But the FDNY still fired him.

Kelly asked the Appellate Division to review Fire Commissioner Nicholas Scoppetta's decision. In November, the court upheld Scoppetta's firing of Kelly.

Three weeks later, Schroeder, who had remained on modified duty while fighting his case, was also fired.

"They all just walked by me like I was a display in a zoo," he said, referring to his last years at the FDNY.